Systems for the preparation of fluids intended to be used for medical treatment purposes are particularly useful for the preparation of dialysis fluid in connection with hemodialysis. However, with minor modifications such systems can also be used for the preparation of replacement fluids in connection with hemofiltration or hemodiafiltration. Those versed in this art will immediately recognize that these systems can thus be used in connection with other methods of treatment in which the mixing of pure water with at least one concentrate is required in order to produce a solution which is preferably entirely bacteria-free and substantially pyrogen-free.
In conventional hemodialysis blood is conducted to one side of a membrane in the dialyzer, and at the same time dialysis fluid is conducted to the opposite side of that membrane. Poisons which one wishes to remove from the blood are in such a case passed from the blood to the dialysis fluid by means of diffusion through the membrane. Under normal circumstances, a certain amount of fluid, primarily water, is at the same time withdrawn through ultrafiltration so that there is some degree of lowering of the patient's weight effected thereby.
Hemodiafiltration differs from hemodialysis most particularly in that a more permeable filter is used and therefore greater ultrafiltration is obtained. This, in turn, makes it necessary for a portion of the ultrafiltrate to be replaced by replacement fluid. In hemofiltration no dialysis fluid is utilized. Instead, with the assistance of a filter, a large quantity of ultrafiltrate is withdrawn, and this must be at least partly replaced by a corresponding quantity of replacement fluid.
Each of these hemodialysis, hemodiafiltration, and hemofiltration processes requires different types of control arrangements to be utilized, but in each of them at least one concentrate is generally mixed with pure water. Certain of these concentrates are of a type which prevent bacterial growth. In that case there are no major problems and the concentrate can be directly mixed with the water. Other concentrates, however, such as those based on bicarbonate, favor bacteria growth and therefore must be filtered, i.e., before they are mixed with the water. The filters used for these purposes are designed for low percolation, which renders the sterilization and/or disinfection required between respective treatments somewhat difficult.